1. Field of the Invention
The present invention relates in general to a marine propulsion system, and more particularly to a propeller shaft assembly for a propulsion system of an outboard drive.
2. Description of Related Art
Many outboard drives of marine watercrafts employ counter-rotational propeller systems which utilize a pair of counter-rotating propellers that operate in series about a common rotational axis. By using propeller blades having a pitch of opposite hands, the dual propeller arrangement provides significant improvement in propulsion efficiency. Such propulsion systems are common in both outboard motors and in stern drive units of inboard/outboard motors.
Counter-rotational propeller systems typically include an inner propeller shaft and a hollow outer propeller shaft through which the inner propeller shaft passes. Under at least one drive condition (e.g., forward drive), the inner shaft rotates in an opposite direction from that of the outer shaft. Commonly, the inner shaft drives a rear propeller and the outer shaft drives an adjacent front propeller.
Some prior counter-rotational propeller systems include a cover to surround the end of the outer propeller shaft to prevent fishing line or weeds from entangling on the inner shaft and damaging oil seals, which are typically disposed between the inner shaft and the outer shaft at the rear end of the outer shaft. As described below in greater detail, such covers are usually positioned between the propeller hubs of the propellers.
Although prior covers disposed over the rear end of the outer shaft generally prevent fishing line and weeds from wrapping around the inner shaft at the interface between the propeller hubs, such covers complicate the propeller shaft assembly, adding to the expense of the drive. Such covers also wear and require replacement, and complicate the process of assembling the propulsion system.